An optical link having an optical transmitter and an optical receiver is useful in applications, where power delivery and/or data transmission via electrical wires is problematic, in particular due to size restrictions of the power delivery and/or data transmission paths. Although the present invention is not limited to a use in medical applications, the present invention will be described herein with respect to medical applications.
There is a clear and ongoing trend to replace conventional surgical procedures with minimally invasive interventions. Reduced trauma, shorter hospital stay and reduced costs are the most important drivers of the adoption of minimally invasive techniques. To enable further innovation in medical instrumentation—thus enabling more advanced and more challenging minimally invasive interventions—there is a need to integrate miniature sensors for in-body imaging and physiological measurement in instruments like catheters and guide wires.
Data and power delivery to the tip of long and thin devices such as a medical catheter or guide wire for imaging, sensing, sensitizing or even ablation can be challenging. Including, on top of that, a high data rate return channel from the distal to the proximal end is even more problematic. This is due to several reasons.
Firstly, the combination of the small cross-section (i.e. small diameter), necessary for the medical intervention, combined with the long length of a guide wire or catheter does severely limit the total number of electrical wires that can be integrated in such an instrument.
Secondly, the integration of multiple electrical wires compromises the flexibility of the instrument, while flexibility is a key property of this type of instruments.
Thirdly, for high data rate, such as e.g. required for an ultrasound transducer at the tip or for sensitive measurements, one often requires coaxial cables which need even more space compared to single-core wires.
Fourthly, instruments with electrical wires typically are not compatible with the use of magnetic resonance imaging due to resonances in/of the electric wiring leading to electromagnetic interference in the connected electronics and also possibly leading to tissue heating. And furthermore, thin electrical cables typically cannot support a relatively high amount of power for use at the distal end of the catheter.
Also, because of their disposable use, catheters and guide wires must be manufactured in a relatively simple and cost-effective way.
Sakaguchi et al.: “19-core fiber transmission of 19×100×172-Gb/s SDM-WDM-PDM-QPSK signals at 305 Tb/s”, Optical Fiber Communication Conference and Exposition, 2012 and the National Fiber Optical Engineers Conference, IEE, 4 Mar. 2012, pages 1-3, report on a free-space coupling system combined with a multi-core fiber enabling upscaling to a record space-division-multiplexed channel number of 19.
Sleiffer et al.: “Mode-division-multiplexed 3×112-Gb/s DP-QPSK transmission over 80-km few-mode fiber with inline MM-EDFA and Blind DSP”, 2012, 38th European Conference and Exhibition on Optical Communications, 16 Sep. 2012, pages 1-3 describe transmission of a 3×112-GB/s DP-QPSK mode-division-multiplexed signal up to 80 km, with and without multi-mode EDFA, using blind 6×6 MIMO digital signal processing.
Roland Ryf et al.; “Mode-Division Multiplexing Over 96 km of Few-Mode Fiber Using Coherent 6×6 MIMO Processing”, Journal of Lightwave Technology, IEEE Service Center, New York, US, vol. 30, no. 4, 1 Feb. 2012, pages 521-531 describe simultaneous transmission of six spatial and polarization modes, each carrying 40 Gb/s quadrature-phase-shift-key channels over 96 km of a low-differential group delay few-mode fiber. U.S. Pat. No. 5,963,349 A discloses an optical wavelength-division multiplexed bidirectional data link using a single multi-mode fiber.
WO 2014/072891 A1 describes an optical link comprising an optical guide through which optical energy is transmitted to a remote distal optoelectronic converter having an optoelectronic device in form of a light emitting diode (LED) which converts the optical energy into electrical energy for powering the optical converter circuit and one or more electronic devices. On the one hand, this known optical link is effective in providing sufficient power delivery capability to actuate an ultrasound catheter, because the optoelectronic device has a large surface area necessary to achieve the necessary power output. On the other hand, the large surface area of the optoelectronic device limits the bandwidth and, hence, the data rate of data transmission. For this reason, it is further proposed there to use a separate optoelectronic device for data transmission in the return path from the distal end to the proximal end. However, a separate optoelectronic device for data transmission and a separate optoelectronic device for energy harvesting add significant complexity to both the electronic and optical part of the interventional instrument using the optical link.
Therefore, there is a need for an improved optical transmitter, optical receiver and optical link which retains the capability of achieving sufficient power output, but increases the bandwidth and data rate in the return path.